This application is based on application no. 2001-261900, filed in Japan on Aug. 30, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a steering control device for an automobile or the like.
2. Description of the Related Art
A conventional steering control device will be described with reference to drawings. FIGS. 17 and 18 show a configuration and an operation of a conventional steering control device disclosed in, for example, Japanese Patent No. 1929781.
In FIG. 17, reference numeral 1 denotes a conventional steering control device, numeral 2 denotes a torque sensor, numeral 3 denotes a vehicle speed sensor and numeral 4 denotes a motor.
In addition, in the figure, the conventional steering control device 1 is provided with steering torque measuring means 91, vehicle speed measuring means 92, motor current measuring means 93, motor average current calculating means 94, motor current storing means 95, motor current determining means 96, electromagnetic clutch controlling means 97, power element controlling means 98 and power element unit for motor drive 99.
As shown in a graph of FIG. 18, the conventional steering control device 1 gradually decreases or increases a motor current (output) according to an average value of motor currents to protect the entire device from heating.
In the above-mentioned conventional steering control device, when a steering once knocks an end, the entire device or a component such as a motor or a control device is heated and a motor current is gradually decreased. As a result, it takes time to cause a motor output torque to return to an initial state.
The present invention has been devised to solve the above-mentioned problem, and it is an object of the present invention to provide a steering control device for eliminating deterioration of steering feeling due to a sudden change of a motor current and further suppressing decrease in an output due to protection against heating by reducing loss in the vicinity of a maximum steering angle of the steering while protecting the device from heating.
In order to attain the above-mentioned object, a steering control device in accordance with the present invention is provided with first motor current limit value calculating means for increasing and decreasing a motor current according to an average value of motor currents over a time period and second motor current limit value calculating means for decreasing a motor current upon determining that a steering is in the vicinity of a maximum steering angle and increasing a motor current upon determining that the steering is not in the vicinity of the maximum steering angle.
In addition, in the steering control device in accordance with the present invention, the second motor current limit value calculating means determines that the steering is in the vicinity of the maximum steering angle to decrease the motor current when a predetermined state quantity is equal to or larger than a first predetermined value and determines that the steering is not in the vicinity of the maximum steering angle to increase the motor current when the predetermined state quantity is equal to or smaller than a second predetermined value.
In addition, in the steering control device in accordance with the present invention, the second motor current limit value calculating means determines that the steering is in the vicinity of the maximum steering angle to decrease the motor current when a predetermined state quantity is equal to or smaller than a first predetermined value and determines that the steering is not in the vicinity of the maximum steering angle to increase the motor current when the predetermined state quantity is equal to or larger than a second predetermined value.
In addition, in the steering control device in accordance with the present invention, the predetermined state quantity is a steering torque.
In addition, in the steering control device in accordance with the present invention, the predetermined state quantity is a steering angle.
In addition, in the steering control device in accordance with the present invention, the predetermined state quantity is a motor current.
In addition, in the steering control device in accordance with the present invention, the f first predetermined value is a saturation value of the motor current.
In addition, in the steering control device in accordance with the present invention, the first predetermined value is a motor current limit value.
In addition, in the steering control device in accordance with the present invention, the first predetermined value is a motor current limit value found by the first motor current limit value calculating means.
In addition, in the steering control device in accordance with the present invention, the predetermined state quantity is a detection value of a motor current.
In addition, in the steering control device in accordance with the present invention, the predetermined state quantity is a steering speed.
In addition, in the steering control device in accordance with the present invention, the steering speed is calculated at least from a motor voltage and a motor current.
In addition, in the steering control device in accordance with the present invention, a motor is controlled with a smaller one of a first motor current limit value found by the first motor current limit value calculating means and a second motor current limit value found by the second motor current limit value calculating means as a limit value of a motor current.
In addition, in the steering control device in accordance with the present invention, determination threshold values indicating that the steering is in the vicinity of the maximum steering angle are the first and the second predetermined values and hysteresis is provided by setting the first and the second predetermined values to be different from each other.
In addition, in the steering control device in accordance with the present invention, the second motor current limit value calculating means determines that the steering is in the vicinity of the maximum steering angle when a first determination condition for determining that the steering is in the vicinity of the maximum steering angle is met for a predetermined time period or more and determines that the steering is not in the vicinity of the maximum steering angle when a second determination condition for determining that the steering is not in the vicinity of the maximum steering angle is not met for a predetermined time period or more.
In addition, in the steering control device in accordance with the present invention, the second motor current limit value calculating means increases or decreases a motor current only when a vehicle speed is equal to or smaller than a predetermined value.
Moreover, in the steering control device in accordance with the present invention, the second motor current limit value calculating means sets an increasing speed of a motor current larger than a decreasing speed.
The steering control device in accordance with the present invention is provided with: motor current detecting means for detecting a motor current; motor voltage detecting means for detecting a motor voltage; a motor driving circuit for driving a motor; and a microprocessor for supplying an applied voltage signal, which is found based on a motor current detection value detected by the motor current detecting means, a motor voltage detection value detected by the motor voltage detecting means, a steering torque detected by a torque sensor and a vehicle speed detected by a vehicle speed sensor, to the motor driving circuit such that the motor driving circuit increases or decreases the motor current according to an average value of motor current detection values over a time period and increases or decreases the motor current by detected that a steering is in the vicinity of a maximum steering angle based on a predetermined state quantity.
Moreover, in the steering control device in accordance with the present invention, the microprocessor comprises: steering speed calculating means for calculating a steering speed based on the motor current detection value and the motor voltage detection value; target current calculating means for calculating a motor current target value based on the detected steering torque, the detected vehicle speed and the steering speed; first motor current limit value calculating means for calculating a first motor current limit value based on the motor current detection value; second motor current limit value calculating means for calculating a second motor current limit value using the predetermined state quantity; motor current limiting means for limiting the calculated motor current target value using the first motor current limit value and the second motor current limit value; and motor current feedback control means for finding a voltage signal applied to the motor such that the limited motor current target value and the motor current detection value coincide with each other.
Other objects and features of the present invention will be apparent from the following descriptions taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.